This invention is concerned with dry powder inhalers for the delivery of drugs to the lungs. In particular, the present invention relates to an inhaler with a chamber containing a medicament or inhalation formulation in the form of powder. The powder is discharged by means of a gas or air stream flowing through the chamber to entrain the powder and to generate or form a powder spray for inhalation.
Many dry powder inhalers are on the market or have been proposed. There are two main types; passive and active. In passive devices all the energy required for deagglomeration the powder and transferring the powder to the lungs is provided by the patient. Most powder inhalers are of the passive type where the powder is inhaled by the patient without the aid of a secondary energy source.
Dry powder inhalers are subdivided into single dose devices and multi dose devices. Multi dose inhalers are further subdivided into pre metered types where the doses are stored individually in the device and metering devices where the powder dose is metered in the device.
Multi dose pre metered devices have the advantage that the single doses are metered under strict factory conditions and the powder can quite easily be isolated from the atmosphere. In many applications the active drug powder is mixed with a carrier such as lactose which tends to absorb humidity from the atmosphere which makes it stick together and difficult to de-agglomerate.
One of the main advantages of active inhalers is that the delivered mass or dose of powder is independent from the flow generated by the user which is generally accepted to be in the range of between 20 to 60 liters per minute. The disadvantage of passive inhalers that the delivered mass or dose varies according to the airflow generated by the user. The present invention is a device that minimizes variations of delivered mass or dose with airflow variations.
Metering powder inhalers have a metering chamber for accurately metering the dose to be delivered while pre metered inhalers have pre-metered doses in capsules or blister or other chambers. For simplification both types will be called metering chambers in this specification. Most passive powder inhalers have a primary flow path for the air that goes through the metering chamber and carries the powder to the patient and a secondary flow path or bypass where the air does not go through the powder-metering chamber.
When the airflow through the chamber containing the powder varies, deagglomeration of the powder and spray generation vary as well. Consequently, the spray characteristics and the amount of outputted powder may very significantly.